1. Field of Invention
This invention relates generally to hydrocarbon extraction and more particularly to a process and apparatus for treating a heavy hydrocarbon feedstock having a specific gravity differential between components of the feedstock.
2. Description of Related Art
Heavy hydrocarbon feedstocks are generally viscous and may be entrained with other components such as rock, sand, clay, and other minerals. As a result, heavy hydrocarbons require processing to separate useful hydrocarbon products from residue before transport and refining.
One example of a heavy hydrocarbon ore deposit is the Northern Alberta oil sands, which comprises about 70 to about 90 percent by weight of mineral solids including sand and clay, about 1 to about 10 percent by weight of water, and a bitumen or oil film. The bitumen may be present in amounts ranging from a trace amount up to as much as 20 percent by weight. Due to the highly viscous nature of bitumen, when excavated some of the ore may remain as clumps of oversize ore, requiring sizing to produce a sized ore feed suitable for processing. The ore may also be frozen due to the northerly geographic location of many oil sands deposits, making sizing of the ore more difficult. The sized ore feed is typically processed by adding water to form a slurry in a location proximate to the ore deposit, and the resulting slurry is hydro-transported through a pipeline to a processing plant for separation of the hydrocarbon products from the sand and other minerals.
Low specific gravity hydrocarbons may be separated from sand and water, which generally have higher specific gravity, by accumulating the feedstock in a separation vessel and allowing gravity separation to occur. Such a separation vessel may have a large diameter relative to side wall height and may include a conical bottom for sand removal. For adequate separation of hydrocarbons, the relatively quiescent conditions of the accumulated feedstock may be required in the vessel, which has the adverse effect of allowing neutral density asphaltene mats to accumulate at an interface between the separated hydrocarbon products and the water. These asphaltene mats accumulate as rag layers and may be difficult to remove.
There remains a need for improved processes and apparatus for treating heavy hydrocarbon feedstocks.